TADS is very thoroughly documented, with several in-depth tutorials and extensive reference material.
Online version at: TADS 3 Bookshelf
Offline version: On the TADS downloads page, under “Other TADS packages → Show full list”, subsection “À la carte components”, there is a link to a download for the full documentation package.
Direct link: http://www.tads.org/t3dl/t3doc.zip